1. Field of the Invention
The invention is concerned with a method for the preparation of stable, cationic latex compositions. The polymer particles comprising the latex have stabilizing, sulfonium cations chemically bound at or near the surface of the particles.
2. Description of the Prior Art
Latexes require some means for providing colloidal stabilization in aqueous media. The usual colloidal stabilization is provided by surfactants which usually are anionic or cationic but may be non-ionic, especially in mixtures with anionic or cationic surfactants. Even though they contribute to the required colloidal stability, the surfactants can interfere with coating performance of the latexes although the amount is limited and less than the desired stability is obtained. Another method is to copolymerize with non-ionic monomers a a small proportion of an ionic monomer to prepare a stable latex with little or no conventional surfactant as described in U.S. Pat. No. 3,637,432. Such processes, however, require special combinations of monomers and special polymerization techniques. Although such processes produce latexes having little or no surfactants, varying amounts of water-soluble products are made during carrying out of the process and remain in the product.
U.S. Pat. No. 3,793,278 describes the reaction of epoxy resins with sulfides and acids, generally in solution to form cationic resins which are then dissolved in water as clear or colloidal solutions. The process is directed to the conversion of relatively low molecular weight resins. Reactions with high molecular weight resins are more difficult because of problems with incompatibility and high viscosity. It would be desirable if a method were available to convert high molecular weight polymers to particles in the form of cationic latexes having cationic charges chemically bound to the particles at or near the particle surface without at the same time forming water-soluble polymeric materials.